Age-related Macular Degeneration (AMD) and especially neovascular AMD (nAMD) is the leading cause of blindness in the developed countries in people ageing over 50 years. An increase in vascular permeability leads to abnormal fluid collection within or below the retina that causes visual dysfunction when it involves the centre of the macula. This leads to rapidly deteriorating acuity, scarring of the pigment epithelium, and permanent visual loss or blindness.
However, intravitreal injection of antiangiogenic agents, including Ranibizumab (trade name Lucentis®, Novartis, Basel, Switzerland), has been shown to significantly improve the course of nAMD. To reduce the burden of intravitreal injections and to optimize the risk/benefit profile, the progression of nAMD features can be monitored noninvasively by Optical Coherence Tomography (OCT). Prominent nAMD features involve the increase of the thickness of retinal structures. Such an increase may be identified when visually comparing two OCT images of the same region of the retina taken at different times, the temporal distance being several days to several months.
For instance, patients treated with Ranibizumab usually undergo an OCT examination every month. If a significant growth in nAMD features is observed, then a treatment decision is indicated: the patient receives a Ranibizumab injection that day, one month later and two months later (treatment phase). Retreatment can be indicated one month later if the nAMD features have not completely receded. Otherwise, the patient does not receive an injection that day, but regularly indicated maintenance injections (maintenance phase).
The OCT acquisition and the subsequent analysis of OCT acquisitions are usually done by skilled personnel, including ophthalmologists. This means that the monitored patients are required to visit a medical practice or specialized unit of a hospital each time an OCT is to be acquired. This puts a considerable burden upon the patients. Furthermore, the frequency of the OCT acquisitions (such as 1 month) is already sort of a compromise between on one hand close monitoring of the development of nAMD and on the other hand the costs and the burden on the patient.
In principle, automatic analysis of OCT acquisitions may alleviate these problems. In recent years, many algorithms have been designed to automatically analyze OCT acquisitions of the retina, cf. Abràmoff MD, Garvin M., Sonka M., Retinal Imaging and Image Analysis, IEEE Rev Biomed Eng. 2010; 3:169-208. In the context of automatic analysis, it is crucial to detect possible imaging errors in order to avoid false negative of false positive results that are exclusively or primarily due to imaging errors. Usually, the signal-to-noise ratio has been employed to provide a measure for the imaging quality. However, this quantity alone usually is not a reliable measure for assessing the reliability of the results of the automatic analysis of the imaging data.